The concentration of glucose in the human bloodstream must be controlled within a relatively tight range (60-120 milligrams per deciliter of blood) to maintain normal health. If blood glucose drops too low, a condition known as hypoglycemia results, with symptoms such as faintness, weakness, headache, confusion and personality changes. Severe hypoglycemia can progress to convulsions, coma and death. Excessive blood glucose, or hyperglycemia, causes excess urine production, thirst, weight loss, fatigue, and in the most severe cases, dehydration, coma and death. Chronic hyperglycemia causes tissue damage due to the chemical reactions between the excess glucose and proteins in cells, tissues, and organs. This damage is thought to cause the diabetic complications of blindness, kidney failure, impotence, atherosclerosis, and increased vulnerability to infection.
The pancreas makes hormones that regulate the concentration of glucose in the blood. Insulin lowers blood glucose levels; when glucose level rises after a meal, the pancreas secretes insulin, which causes muscle and other tissues to take up glucose from the blood stream. Glucagon raises blood glucose levels; when blood glucose levels fall, the pancreas secretes glucagon to signal the liver to make stored glucose available.
A third glucose-regulating hormone, amylin, was discovered in 1987. Physiologists now generally consider that all three hormones play a role in the complex aspects of glucose metabolism. The chemical structure of amylin and its metabolic action on muscle and pancreas tissue has recently been elucidated. Amylin is said to work with insulin to moderate the glucose-lowering effects of insulin under certain circumstances, to help replenish liver glycogen after a meal, and to encourage the synthesis of fat from excess glucose. As a result, amylin, like glucagon, can raise the blood glucose level.
Diabetes mellitus is associated with continuous and pathologically elevated blood glucose concentration; it is one of the leading causes of death in the United States and is responsible for about 5% of all mortality. Diabetes is divided into two major sub-classes: Type I, also known as juvenile diabetes, or Insulin-Dependent Diabetes Mellitus (IDDM), and Type II, also known as adult onset diabetes, or Non-Insulin-Dependent Diabetes Mellitus (NIDDM).
According to the American Diabetes Association, there are over one million juvenile diabetics in the United States. Diabetes is a form of autoimmune disease. Autoantibodies produced by the patients completely or partially destroy the insulin producing cells of the pancreas. Juvenile diabetics must, therefore, receive exogenous insulin during their lifetime. Without treatment, excessive acidosis, dehydration, kidney damage, and death may result. Even with treatment, complications such as blindness, atherosclerosis, and impotence can occur.
There are more than five million Type II (adult onset) diabetics diagnosed in the United States. Type II disease usually begins during middle age; the exact cause is unknown. In Type II diabetics, rising blood glucose levels after meals do not properly stimulate insulin production by the pancreas. Additionally, peripheral tissues are generally resistant to the effects of insulin. The resulting high blood glucose levels (hyperglycemia) can cause extensive tissue damage. Type II diabetics are often referred to as insulin resistant. They often have higher than normal plasma insulin levels (hyperinsulinomia) as the body attempts to overcome its insulin resistance. Some researchers now believe that hyperinsulinomia may be a causative factor in the development of high blood pressure, high levels of circulating low density lipo-proteins (LDLs), and lower than normal levels of the beneficial high density lipo-proteins (HDLs). While moderate insulin resistance can be compensated for in the early stages of Type II diabetes by increased insulin secretion, in advanced disease states insulin secretion is also impaired. Treatments of Type II diabetes preferably address both insulin resistance and faulty insulin secretion.
Insulin resistance and hyperinsulinomia have also been linked with two other metabolic disorders that pose considerable health risks: impaired glucose tolerance and metabolic obesity. Impaired glucose tolerance is characterized by normal glucose levels before eating, with a tendency toward elevated levels (hyperglycemia) following a meal. According to the World Health Organization, approximately 11% of the U.S. population between the ages of 20 and 74 are estimated to have impaired glucose tolerance. These individuals are considered to be at higher risk for diabetes and coronary artery disease.
Obesity may also be associated with insulin resistance. A causal linkage among obesity, impaired glucose tolerance, and Type II diabetes has been proposed, but a physiological basis has not yet been established. Some researchers believe that impaired glucose tolerance and diabetes are clinically observed and diagnosed only later in the disease process after a person has developed insulin resistance and hyperinsulinomia.
Insulin resistance is frequently associated with hypertension, coronary artery disease (arteriosclerosis), and lactic acidosis, as well as related disease states. The fundamental relationship between these disease states, and a method of treatment, has not been established.
Insulin and sulfonylureas (oral hypoglycemia therapeutic agents) are the two major classes of diabetes medicines prescribed today in the United States.
Insulin is prescribed for both Type I and Type II diabetes, while sulfonylureas are usually prescribed for Type II diabetics only. Sulfonylureas stimulate natural insulin secretion and reduce insulin resistance; these compounds do not replace the function of insulin in metabolism. Approximately one-third of patients who receive sulfonylurea become resistant to it. Some Type II diabetics do not respond to sulonylurea therapy. Of patients who do respond to initial treatment with sulfonylureas, 5-10% are likely to experience a loss of sulfonylurea effectiveness after about ten years.
Insulin itself has a relatively narrow therapeutic window. Relatively high insulin doses can produce hypoglycemic shock as the blood glucose drops too low. Low or infrequent doses may result in hyperglycemia.
In Europe, two other classes of oral hypoglycemic agents are available, i.e., biguanides and alpha-glucosidase inhibitors. Biguanides work by reducing glucose production in the liver and limiting glucose absorption. Although biguanides are also used in Canada, they are banned in the U.S. due to increased incidence of mortality. Alpha-glucosidase inhibitors are sold in certain European countries, but have not obtained FDA approval for use in the U.S. These drugs reduce high blood glucose levels by slowing the uptake of ingested foods. Side effects include flatulence, diarrhea, and abdominal pain.
U.S. Pat. No. 4,761,286 to Hiji discloses that an aqueous extract derived from the leaves of Gymnema sylvestre can be utilized in combination with a foodstuff that is absorbed as glucose by the intestinal tract so as to inhibit glucose absorption. Chatterji, International Patent Application No. WO 95/10292, reported that glucose metabolism in a human patient can be effectively modulated by oral administration of an extract derived from the leaves of G. sylvestre in combination with a bio-inert polysaccharide, i.e., a polysaccharide that is non-metabolizable by the patient. Heretofore the inhibitory action on the absorption of sugar in the intestinal tract by G. Sylvestre extracts has been attributed to gymnemic acid and the varius derivatives thereof present. See, for example, U.S. Pat. No. 5,137,921 to Kensho et al. and Shimizu et al., J. Vet. Med. Sci. 59(4):245-251 (1997).
It has now been found, however, that glucose metabolism in a human patient can be effectively modulated by oral administration of gurmarin, a polypeptide; optionally in combination with a non-metabolizable polysaccharide.